In petroleum oil refinery processes refinery sludges are normally produced which contain various proportions of oil mixed with small amounts of solids and relatively large quantities of water. Sludges from various refinery processes are frequently mixed together. A composite sludge, for example, might contain by weight 2-4% solids, 6-51% oil and the remainder water.
These sludges are frequently produced in what is referred to as a dissolved air flotation process (DAF) where a chemical is added to waste water containing oil and solids and the water is treated with air under pressure. The air causes the solids and oil to float upward and the resultant sludge is raked out. The problem with which the present invention is concerned is the separation of the oil and water from the subject sludge.
High molecular weight polymeric flocculants have heretofore been employed in dewatering refinery DAF sludges. An example of such a process is one where the flocculant is added to a sludge which is then dewatered on a belt-type filter press. Substantial oil recovery has been achieved by this type of process. However, the results are apt to be erratic because there is no reliable method for screening the products for dewatering and enhancement of oil recovery on a sludge belt filter press (BFP).
It is, therefore, an object of this invention to provide a process of recovering oil from oil containing sludges, and especially sludges from petroleum refining, which enhances oil recovery and also increases the rate of dewatering.